1. Field of the Invention
The present invention is directed to intermetallic compounds of transition metal oxide alkoxides. More particularly, the instant invention is directed to intermetallic compounds useful as catalyst components in the polymerization of alpha-olefins.
2. Background of the Prior Art
It has been recently discovered that an important class of intermetallic compounds can be utilized as catalyst components in the polymerization of alpha-olefins, particularly ethylene, to produce a linear low density polyethylene resin.
Specifically, U.S. Pat. No. 4,513,095, assigned to the assignee of the present application, provides a linear low density polyethylene resin (LLDPE) in a low pressure polymerization process in which the LLDPE has a narrow molecular weight distribution, improved strength properties, high melt viscosity, high softening point, improved environmental stress crack resistance and improved low temperature brittleness. These properties manifest themselves in improved blown films, wire and cable coatings, cast films, coextrusions, and injection and rotational molding applications.
The intermetallic compound of the '095 patent is formed by the reaction of a transition metal oxide alkoxide with at least one reducing metal, i.e., a metal having a higher oxidation potential than the transition metal. In a preferred embodiment of this patent, polymeric titanium alkoxide, or oxoalkoxide, is reacted with magnesium metal to provide a reaction product which is activated to form the olefin polymerization catalyst element. In a still more preferred embodiment of the invention set forth in the '095 patent, titanium tetrabutoxide is reacted with magnesium metal in a hydrocarbon solvent and in the presence of a controlled source of water, preferably a hydrated metal salt such as magnesium halide hexahydrate.
Although the intermetallic compound of U.S. Pat. No. 4,513,095 utilized as a catalyst component with an organometallic compound, preferably, an aluminum alkyl, more preferably, trialkyl aluminum and most preferably, triethyl aluminum, produces improved linear low density polyethylene resins having narrow molecular weight distribution, improved strength properties, higher melt viscosity, higher softening point, improved environmental stress crack resistance and improved low temperature brittleness and even though excellent catalyst efficiency is obtained using this catalyst still further improvements in catalyst efficiency are always desirable. As those skilled in the art are aware, increased catalyst efficiency decreases an important expense in the process of forming the polyethylene resin, the cost of catalyst. In addition, increased catalyst efficiency decreases the cost of separating the catalyst from the product since less catalyst is required to produce the same quantity of polymer. Finally, the polymeric product properties are enhanced because, with the presence of a lower concentration of catalyst in the polymerization reaction mixture, the level of catalyst impurity remaining in the final resin product is correspondingly decreased. As such, decreased level of catalytic impurity increases product properties which, as those skilled in the art are aware, are adversely affected in proportion to the degree of catalyst concentration in the polymer.